Identical twins separated at birth in a social experiment have been reunited after 35 years.

And while the man behind the test has been widely criticised, Elyse Schein and Paula Bernstein appear to have answered the question of what is more influential - nature or nurture.

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Elyse Schein and Paula Bernstein - the pair of identical twins separated at birth as part of a social experiment

Both are writers who edited their school newspapers and studied film at university, and both fulfilled lifelong dreams to travel to Paris.

"Since meeting Elyse, it is undeniable that genetics play a huge role - probably more than 50 per cent," Paula told National Public Radio in the US.

"It's not just our taste in music or books; it goes beyond that.

"In her, I see the same basic personality and yet, eventually, we had to realise that we're different people with different life histories."

The twins were reunited after Elyse contacted authorities in 2004 in an attempt to meet her birth mother.

The request was denied as the woman had died in the mid-1970s, but the social worker informed Elyse she was an identical twin - and she was reunited with Paula within days.

"We had 35 years to catch up on," Paula said of the meeting that started at lunch and ran well into the night.

"How do you start asking somebody, 'what have you been up to since we shared a womb together?'

"Where do you start?"

An obvious question once the twins had gotten acquainted was to find out why they were separated.

Elyse already knew: they were the subject of a study by internationally-renowned child psychiatrist Peter Neubauer, who had arranged the experiment through the twins' adoption agency.

He was assisted by an agency consultant and child psychologist, who believed that twins should be raised separately to improve their psychological development and that dressing and treating them the same "retarded their minds".

The couples who adopted each of the twins soon after their birth in 1968 were not informed their girls had an identical sister and knew only that their children were the subject of an ongoing study.

The twins tracked Mr Neubauer down and, after initially refusing to speak to them, he agreed to meet them on the condition that they not record their conversation.

The esteemed Yale academic allegedly showed no remorse and offered no apology for separating the sisters for research purposes, and he has prohibited the public release of his study of them until 2066.

"It's kind of disturbing to think that all this material about us is in some filing cabinet somewhere," Paula said.

The twins - who are now also near-neighbours - have utilised their shared skills by writing a book, Identical Strangers.

Both veer between regret at the years lost and joy at discovering each other.

"That life never happened and it is sad that, as close as we are now, there is no way we can ever compensate for those 35 years," Paula said.

"It is hard to see where we are going to go, it's really uncharted territory," Elyse added.

"But I really love Paula and I can't imagine my life without her."